1. Prior Art
The following is a tabulation of some prior art that presently appears relevant:
U. S. patentsPat. No.Issue DatePatentee7423650Sep. 9, 2008Lee et al.
2. Description of the Related Art
In the animation industry today, there are currently two general methods of producing animation: the 2D method, and the 3D method. Animation created using the 2D method is often referred to as 2D animation. Animation created using the 3D method is often referred to as 3D animation.
Using the 2D method, an artist creates 2D characters to be animated by producing two-dimensional drawings, or art assets, using a flat medium. This flat medium could be paper, or an acetate animation cell, or two-dimensional drawing software such as Adobe Illustrator or Adobe's CS5 Flash authoring tool. Using the 3D method, an artist creates 3D characters to be animated by producing numerical models that define an armature or skeleton for a character and the geometry of the character using a three-dimensional coordinate system. 3D character definitions are typically created using three-dimensional modeling software tools such as Autodesk's Maya or 3ds Max, and are typically stored as digital files in a computer memory.
When animation is created using a computer, whether using the 2D or 3D methods, animators typically produce character animation sequences using a process called key framing. In the key framing process, animators use software to create key frames that define the position and orientation of various body parts of the character to be animated at various points in time. In an animated sequence that runs at a rate of 24 frames per second for 72 frames, for example, an animator might create one key frame on the first frame in order to define the position and orientation of the character's various body parts at the start of the sequence, another key frame at the 12th frame in order to define the position and orientation of the character's various body parts one half-second into the animation sequence, and so on, until the motion for the character for the entire 72 frames of the sequence has been defined.
Once the key frames for an animation sequence have been defined, the software that produces the final animation uses a process called in-betweening to determine the position and orientation of each body part in all the frames of the animation by interpolating between the body part positioning and orientation defined in the key frames. In this way, the software produces the continuous motion of the animated character.
The process of key framing is similar for 2D animation and 3D animation, however, in 2D animation, positioning and orientation of 2D drawings are defined using a two-dimensional coordinate system, whereas in 3D animation, positioning and orientation of three-dimensional armatures are defined using a three-dimensional coordinate system, with an additional depth, or “z” coordinate added.
Both the 2D and 3D animation methods are commonly used in commercial animation ventures such as television programs, movies and video games. Each method has certain advantages and is appropriate for certain types of applications. However, the results of each method are very different in their appearance.
But although the 2D animation method produces results that have an appearance that is often desirable for animation customers and animation producers, the process of producing 3D animation has several distinct advantages over the process of producing 2D animation in terms of the ease of production and the quality of results:
One advantage that the 3D animation method has over the 2D animation method is that it can be used to easily create animation sequences that can depict an animated character from any number of different angles or vantage points. 2D animation methods typically involve creating animation sequences that show an animated character from one particular vantage point or view angle. For example, a 2D animation producer might produce an animation that depicts a character that is running in a specific direction. If the animation producer then also wished to show the same character running as seen from a different vantage point or orientation, then he or she would have to produce a second set of drawings and a second animation sequence depicting the action as seen by the second view. Likewise, any additional desired angles would require additional art and animation sequences to be produced.
The 3D animation method, by contrast, produces a single animation sequence that is not associated with any particular viewing angle or vantage point. By defining and moving a virtual camera in three-dimensional space, 3D animation software can use this single animation sequence to produce a character animation that shows the character as seen from any particular viewing angle or vantage point.
A second benefit of the 3D animation method over the 2D animation method is that with the 3D animation method, the character that is being animated, as defined by the 3D numerical model as described above, is usually defined distinctly and separately from the sequence of movements that are applied to that model in an animation sequence. In 3D animation, a single key frame-defined animated sequence can be applied to any character, or model. This means that if an artist has defined two different models representing two different characters, that the same key frame-defined sequence could be applied to either model, and an animation of either character performing the same animation motion could be produced using one single animation sequence.
In 2D animation, by contrast, the animation sequence, which defines the way the character moves, is typically not separable from the graphical visual information which defines the way the character looks, as implemented by the 2D drawings as stated above. Typically, in 2D animation, therefore, each character must be animated separately.
A third benefit of the 3D animation method over the 2D animation method is that it is often possible for an animator of a certain level of skill to produce results that are superior in terms of the realism and accuracy of movement using the 3D method as opposed to the 2D method. If, for example, an animator is animating a character that is running towards the camera, then a considerable amount of foreshortening of the limbs will be in evidence at various points throughout the animation cycle. Using the 2D animation method, considerations of the foreshortening and occlusion of the limbs of the character at any given moment in time must be estimated by the artist in a process that requires a considerable amount of judgment and skill in order for the results to be completed effectively. Using the 3D method, by contrast, in which limbs are positioned and oriented in three-dimensional space, foreshortening of the limbs and the occlusion of some limbs by other limbs at various points in time within the animation cycle are precisely determined by the rendering software, and the result is a mathematically accurate depiction of the character as rendered from a specific vantage point at a specific point in time. Animation sequences created by animators using the 3D method often have a more naturalistic and realistic appearance than animation sequences produced by animators of comparable skill using the 2D method.
Because of the above stated advantages of the 3D animation method, it is desirable for animation producers to be able to create 2D animation sequences in a way that utilizes and exploits the benefits of 3D technology, while at the same time, producing an animation where the end results have the appearance of 2D animated scenes in which animated characters are visually defined using 2D drawings rather than 3D numerical models, but where the movement is defined using the advantageous 3D method.
In U.S. Pat. No. 7,423,650, (2008), Lee et al. propose a method of representing and animating a two-dimensional humanoid character in three-dimensional space. This method attempts to leverage some of the advantages of the 3D method described above in order to produce a 2D animation by using “a method that can represent a 2D humanoid character according to views of the humanoid character taken by a camera in a 3D space and animates the 2D humanoid character according to a procedure of a 3D animation.” However, the method described has a number of deficiencies and drawbacks.
The method described by Lee et al. claims a preprocessing operation, which includes a motion database setup operation that involves “analyzing a 3D character animation of the 3D humanoid character, extracting mapping information that maps the 3D character animation into a 2D character animation, and storing the mapping information in a motion database.” This preprocessing operation presents a number of disadvantages: The first disadvantage is that the method requires that a set of finite pre-determined virtual camera angles or views be used in order to compute and populate the motion database. This results in limiting implementations of the method to only be able to produce 2D character animation sequences based on these pre-determined camera angles. This limitation would pose a disadvantage in real-time implementations such as video games, where user control over animated characters necessitates the ability to render animated characters from arbitrary and unpredictable angles in order to create a continuous and believable experience.
A second disadvantage of this preprocessing operation is that it would produce significantly large data sets, and would require access to the database for access to these data set in order for implementations to function. This would limit the usefulness of some implementations, such as online video gaming or virtual reality implementations, due to data transmission requirements.
The method described by Lee et al. also fails to describe a selection operation which selects from among a set of views of any particular body part on a frame-by-frame basis in order to produce an optimally continuous 2D animated sequence. To illustrate, FIG. 1 shows a number of views of a human head, a front view 200a, right ¾front view 200b, right side view 200c, right ¾back view 200d, back view 200e, right ¾left view 200f, left side view 200g, left ¾front view 200h, and top view 200i. If a 3D animated sequence contained one key frame in which the head of the character were positioned, relative to a specific virtual camera in 3D space, so that the view of the head were best represented by the right side view 200c, and a second key frame some number of frames later where the head of the character where positioned so that the view of the head were best represented by the left side view 200g, then the most optimal implementation would provide a selection operation that operates between key frames that would cause the representation of the head to smoothly migrate over time over adjacent representations of the head between the key frames. To illustrate given the example above, the head might be represented by the right side view 200c in one frame of the animation sequence, then by the right ¾back view 200d at a subsequent frame, then by the back view 200e at a further subsequent frame, then by the right ¾left view 200f at a further subsequent frame, and finally, the left side view 200g as the sequence progresses toward the second key frame. The method described by Lee et. al does not describe or teach this frame-by-frame selection process, but, rather, describes a process in which art assets are selected on a per key-frame basis. Given the example above, this would cause the situation where the head, which was represented by right side view 200c in one frame, would in a later frame, be represented by the left side view 200g, and because these two views are not visually adjacent, it would cause the animation to have a jerky and discontinuous appearance.